title: High temperature causes negative whole-plant carbon balance under mild drought.
abstract: Theoretically, progressive drought can force trees into negative carbon (C) balance by reducing stomatal conductance to prevent water loss, which also decreases C assimilation. At higher temperatures, negative C balance should be initiated at higher soil moisture because of increased respiratory demand and earlier stomatal closure. Few data are available on how these theoretical relationships integrate over the whole plant. We exposed Thuja occidentalis to progressive drought under three temperature conditions (15, 25, and 35°C), and measured C and water fluxes using a whole-tree chamber design. High transpiration rates at higher temperatures led to a rapid decline in soil moisture. During the progressive drought, soil moisture-driven changes in photosynthesis had a greater impact on the whole-plant C balance than respiration. The soil moisture content at which whole-plant C balance became negative increased with temperature, mainly as a result of higher respiration rates and an earlier onset of stomatal closure under a warmer condition. Our results suggest that the effect of drought on whole-plant C balance is highly temperature-dependent. High temperature causes a negative C balance even under mild drought and may increase the risk of C starvation.
authors.affiliation: Max Planck Institute for Biogeochemistry, Jena, 07745, Germany.|Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, 666303, China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Junbin
authors.initials: J
authors.lastname: Zhao
authors.affiliation: Max Planck Institute for Biogeochemistry, Jena, 07745, Germany.
authors.forename: Henrik
authors.initials: H
authors.lastname: Hartmann
authors.affiliation: Max Planck Institute for Biogeochemistry, Jena, 07745, Germany.
authors.forename: Susan
authors.initials: S
authors.lastname: Trumbore
authors.affiliation: Max Planck Institute for Biogeochemistry, Jena, 07745, Germany.
authors.forename: Waldemar
authors.initials: W
authors.lastname: Ziegler
authors.affiliation: Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, 666303, China.
authors.forename: Yiping
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D019069:Cell Respiration; D055864:Droughts; D006358:Hot Temperature; D010788:Photosynthesis / Q000502:physiology; D054046:Plant Stomata / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology*; D012987:Soil; D029783:Thuja / Q000502:physiology*; D014197:Trees; D014867:Water / Q000502:physiology*
chemical_list: D012987:Soil; D014867:Water; D002245:Carbon Dioxide; D002244:Carbon
keywords: carbon compensation point; carbon limitation; drought; high temperature; whole-plant chamber